Definition
In maritime and civil law, jactus is the deliberate throwing of cargo overboard to lighten or save a vessel in peril. The term derives from the Latin jacere (to throw) and refers specifically to the act of jettisoning goods at sea — not accidental loss, but a voluntary sacrifice made to preserve the ship and remaining cargo from a common danger. Goods lost by jactus are a proper subject for general average contribution, meaning the loss is shared proportionally among all parties whose property was saved by the sacrifice.
The term also appears in a compound form: jactus lapilli, the throwing down of a stone, which under Roman civil law was one recognized method of interrupting prescription — that is, of breaking the running of an acquisitive time period against a landowner when another party was building encroachingly on his land.
Common Confusion
Jactus and jettison are functionally equivalent terms in most legal contexts, and Anderson's Dictionary simply redirects jactus to JETTISON. The distinction worth preserving is register: jactus is the civil law and historical term drawn from Roman sources, while jettison is the common law and modern maritime term in active use. Researchers encountering jactus in older admiralty materials should understand they are reading the civilian vocabulary that shaped general average doctrine before common law courts absorbed and anglicized the concept. The underlying legal rule is the same; the label signals the source tradition.
Why It Matters in Research
Jactus is a term that functions primarily as a gateway to larger doctrines rather than as a freestanding rule. Researchers encountering it in historical sources should follow two threads:
First, general average. The significance of jactus is not the act of throwing goods overboard but the legal consequence — that the loss does not fall entirely on the owner of the sacrificed goods. The principle that a voluntary sacrifice for the common benefit should be shared by all who benefit from it is ancient, traceable to the Lex Rhodia (Rhodian sea law), referenced in the Digest at 14.2. When reading eighteenth- and nineteenth-century admiralty cases or treatises, jactus will appear as the triggering event for general average calculations. Researchers should move from jactus into the general average literature to understand contribution rules, adjustment procedures, and the evolution of the York-Antwerp Rules.
Second, the jactus lapilli usage is narrow but historically important for property and prescription research. It appears in civil law contexts involving interference with another's building on your land and the mechanics of interrupting acquisitive prescription. This sense of jactus will not appear in common law materials and is essentially confined to civilian and mixed-jurisdiction sources.
A trap for corpus researchers: Burrill's entry for jactus is split across two distinct definitions that appear under the same headword — one for the old practice sense of "thrown" or "overthrown" (as in a defeated plea), and one for the maritime jettison sense. This reflects the broader range of the Latin root and means that not every instance of jactus in a legal text refers to maritime sacrifice. Context is essential.
Historical Dictionary Support
The historical dictionaries converge on the maritime meaning as primary. Black's (both editions) defines jactus by reference to the Digest's Rhodian sea law title and connects it directly to general average — the core practical consequence. Black's second edition adds a citation to Barnard v. Adams, 10 How. 308 (1850), a genuine U.S. Supreme Court case on general average that provides a working illustration of how the jactus principle operated in American admiralty courts.
Anderson's treats jactus as purely synonymous with jettison, which is defensible for practical research purposes but loses the civilian lineage. Burrill offers the most complete picture by acknowledging both the maritime/civil law meaning and the older Latin usage meaning simply "thrown" or "defeated," a reminder that jactus had procedural applications beyond maritime law in the Roman sources.
None of the historical dictionaries develop the jactus lapilli sense at length. Black's second edition mentions it in passing within the main entry, but researchers needing to work with that concept in civil law or prescription contexts will find the historical dictionary treatment thin and should turn to treatises on Roman property law or civil law prescription directly.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: General Average; Jettison; Lex Rhodia